JP7347192B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

In image forming apparatuses, when paper is conveyed, a phenomenon in which the position of the paper shifts in a direction perpendicular to the paper conveyance direction (hereinafter also referred to as the "paper width direction"), that is, the paper is skewed, may occur. be. If an image is formed on the paper while the paper is skewed, the position of the image on the paper will be shifted. For this reason, the amount of misalignment of the paper in the paper width direction (hereinafter also referred to as the "amount of misalignment") is detected by a misalignment detection sensor, and the misalignment is corrected by moving the paper in a direction that cancels out the detected amount of misalignment. Techniques for correcting this have been proposed.

In addition, Patent Document 1 discloses that when performing so-called reprint printing, in which an image is printed on paper on which an image has been formed in advance, an offset detection sensor is used to accurately detect the edge position of the paper. The paper is read by the image reading unit, and it is determined whether or not there is an image at the position to be detected for the amount of deviation, and if there is an image at the position to be detected for the amount of deviation, it is determined whether the A technique for resetting the distance is described.

Japanese Patent Application Publication No. 2015-43024

However, with the technology described in Patent Document 1, it is necessary to have the image reading unit read the paper for additional printing each time before starting additional printing, so it takes time and effort to reset the predetermined distance. .

The present invention has been made to solve the above-mentioned problems, and its purpose is to re-set a predetermined distance for misalignment detection without having an image reading unit read the paper before printing. The objective is to provide an image forming apparatus that can.

The image forming apparatus according to the present invention uses an image forming section that forms an image on a sheet of paper, and an offset detection sensor that is disposed upstream of the image forming section in the sheet conveying direction. a deviation detection unit that outputs the amount of deviation in the width direction of the paper at a position separated by a predetermined distance; and a control unit that aligns the paper and the image by correcting deviation according to the amount of deviation. As a result of outputting the amount of deviation by the deviation detection sensor at a predetermined distance set in advance, if the control unit determines that deviation correction cannot be performed, the control unit changes the predetermined distance and corrects the deviation again. The detection sensor outputs the amount of deviation, and the predetermined distance is reset based on the output result.

According to the present invention, the predetermined distance for detecting deviation can be reset without having the image reading unit read the paper before printing.

1 is a schematic diagram showing an example of the overall configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a plan view showing the configuration of a deviation detection section and a positioning section. FIG. 3 is a diagram of the configuration of the offset detection section viewed from the upstream side in the paper conveyance direction. FIG. 3 is a diagram illustrating the amount of paper deviation detected by a deviation detection sensor and the correction of paper deviation based on this deviation amount. FIG. 3 is a diagram illustrating a detection compatible area of a deviation detection sensor. FIG. 3 is a diagram showing sensor output of a deviation detection sensor. FIG. 6 is a diagram illustrating an example of a sensor output when there is paper dust or the like near the edge of the paper. FIG. 7 is a diagram illustrating an example of sensor output when additional printing is performed. FIG. 1 is a block diagram illustrating a configuration example of a control system of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a diagram showing an example of a setting screen displayed on the operation display section. 12 is a flowchart (Part 1) illustrating an example of a process including detecting the amount of deviation and resetting a predetermined distance. 12 is a flowchart (Part 2) illustrating an example of a process including detecting the amount of deviation and resetting a predetermined distance.

Embodiments of the present invention will be described in detail below with reference to the drawings. In this specification and the drawings, components having substantially the same functions or configurations are designated by the same reference numerals, and redundant explanation will be omitted.

<Configuration of image forming configuration>
FIG. 1 is a schematic diagram showing an example of the overall configuration of an image forming apparatus according to an embodiment of the present invention.
As shown in FIG. 1, the image forming apparatus 10 includes a paper feeding section 12 that supplies paper, an image forming section 14 that forms an image on the paper, a paper discharge section 16 that discharges the paper, and a control section 17. It includes an image reading section 18 that reads an image of a document, and an operation display section 20 that serves as a user interface. In this embodiment, as an example, a case will be described in which the image forming apparatus 10 is a tandem color image forming apparatus that performs image forming processing (printing processing) based on an electrophotographic method.

The paper feed section 12 is provided with three paper feed trays 12a, 12b, and 12c and a paper feed conveyance path 36. Paper used for image formation (printing) is stored in each of the paper feed trays 12a, 12b, and 12c. Further, each of the paper feed trays 12a, 12b, and 12c stores paper (standard paper, etc.) that is identified by paper size. Each of the paper feed trays 12a, 12b, and 12c supplies paper of a size specified by a user in a print job or the like, or of a size automatically selected according to the size of a document. The paper feed conveyance path 36 is a conveyance path for conveying paper supplied from any one of the paper feed trays 12a, 12b, and 12c.

The paper discharge section 16 discharges the paper conveyed via the image forming section 14 to a predetermined tray. The paper discharge section 16 is provided with a paper discharge conveyance path 38 . A conveyance path switching section 27 is provided in the middle of the paper discharge conveyance path 38 . Further, the paper discharge section 16 is provided with a main tray 31m and a subtray 31s. The transport path switching unit 27 switches between the main tray 31m and the sub tray 31s to which the paper is to be ejected.

The image reading unit 18 includes an automatic document feeder 18a called an ADF (Auto Document Feeder) and a document image scanning device (scanner) 18b. The automatic document feeder 18a uses a conveyance mechanism to convey the document placed on the document tray and sends it to the document image scanning device 18b. The image reading unit 18 can continuously read images of a large number of originals placed on the original tray by cooperation of the automatic original feeding device 18a and the original image scanning device 18b. The document image scanning device 18b optically scans the document conveyed onto the contact glass by the automatic document feeder 18a or the document placed on the contact glass, and converts light reflected from the document into a CCD (Charge Coupled Device). ) The image of the document is read by forming an image on the light-receiving surface of a sensor, etc. The image reading unit 18 generates image data based on the reading result by the original image scanning device 18b. This image data is subjected to predetermined image processing by an image processing section 11, which will be described later.

The operation display unit 20 is configured using, for example, a liquid crystal display (LCD) with a touch panel. The operation display section 20 functions as a display section 20a and an operation section 20b. The display unit 20a displays various operation screens, setting screens, image status display, operating status of each function, etc. in accordance with display control signals input from the control unit 17. The operation unit 20b includes various operation keys such as a numeric keypad and a start key, receives various input operations from the user, and outputs operation signals to the control unit 17. The user can operate the operation display section 20 to perform various settings related to image formation, such as document settings, image quality settings, magnification settings, application settings, output settings, single-sided/double-sided settings, and paper settings.

The image forming section 14 forms an image on a sheet of paper fed from one of the paper feed trays 12a, 12b, and 12c through the paper feed conveyance path 36. The image forming section 14 includes four photoreceptor units 22Y, 22M, 22C, and 22K corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K). The photoreceptor unit 22Y forms a yellow toner image on the surface of a drum-shaped photoreceptor that is an image carrier. Although not shown, the photoreceptor unit 22Y includes a charger, an exposure device, a developer, a primary transfer roller, a cleaner, and the like. The charger charges the surface of the photoreceptor to a predetermined potential. The exposure device forms an electrostatic latent image on the surface of the photoreceptor by scanning the surface of the photoreceptor charged by the charger with a laser beam. The developing device forms a yellow toner image on the surface of the photoreceptor by supplying yellow toner to the surface of the photoreceptor on which an electrostatic latent image is formed by the exposure device. The primary transfer roller transfers (primary transfer) the toner image formed on the surface of the photoreceptor to the intermediate transfer belt 24 through development processing (toner supply processing) using a developing device. The cleaner removes toner remaining on the surface of the photoreceptor after passing through the primary transfer roller. The other photoreceptor units 22M, 22C, and 22K have the same configuration as the photoreceptor unit 22Y, except that the color of toner supplied by the developing device is different.

The intermediate transfer belt 24 is supported in a loop shape by a plurality of belt support rollers (not shown). One of the plurality of belt support rollers that support the intermediate transfer belt 24 serves as a driving roller for rotating the intermediate transfer belt 24 in the direction of the arrow. The intermediate transfer belt 24 is placed in contact with the surface of the photoreceptor of each of the photoreceptor units 22Y, 22M, 22C, and 22K. The yellow toner image formed by the photoreceptor unit 22Y is transferred to the intermediate transfer belt 24 (primary transfer) by a primary transfer roller (not shown) that sandwiches the intermediate transfer belt 24 between the photoreceptor of the photoreceptor unit 22Y. be done.

When forming a color image, a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image are created by primary transfer rollers corresponding to each photoreceptor unit 22Y, 22M, 22C, and 22K. are sequentially transferred onto the intermediate transfer belt 24 in an overlapping manner. As a result, a color toner image is formed on the intermediate transfer belt 24.

A secondary transfer section 26 is provided downstream of the photoreceptor unit 22K in the moving direction of the intermediate transfer belt 24. The secondary transfer section 26 transfers (secondary transfer) the toner image transferred onto the intermediate transfer belt 24 by the above-mentioned primary transfer roller onto a sheet of paper (secondary transfer). The secondary transfer section 26 is configured using a secondary transfer roller.

The image forming section 14 includes the above-described photoreceptor units 22Y, 22M22C, 22K, intermediate transfer belt 24, primary transfer roller, secondary transfer section 26, and the like. Further, the image forming section 14 is provided inside the image forming apparatus main body 30.

A paper conveyance path 32 is provided in the image forming apparatus main body 30 . A plurality of conveyance rollers 34 are provided in the paper conveyance path 32. Each conveyance roller 34 conveys the paper along the paper conveyance path 32. The paper transport path 32 is connected to a paper feed transport path 36 provided in the paper feed section 12 and a paper discharge transport path 38 provided in the paper discharge section 16 . The paper supplied from the paper feed section 12 is conveyed along the paper conveyance path 32 from the right side to the left side in FIG. Therefore, the paper conveyance direction is the Y direction. Although not shown in FIG. 1, the paper transport path 32 includes a reversing transport path for reversing the front and back sides of the paper, and a reversing transport path for transferring the reversed paper to the secondary transfer unit 26 of the image forming unit 14. It has a re-conveyance path for conveying it again towards the destination.

A fixing section 40 is provided downstream of the secondary transfer section 26 in the paper conveyance direction. The fixing section 40 fixes the toner image transferred onto the paper by the secondary transfer section 26 onto the paper by heating and applying pressure. The fixing unit 40 includes a heating roller 40a that includes a built-in heater and the like, and a pressure roller 40b that contacts the heating roller 40a with a predetermined pressing force. A fixing nip is formed at the contact area between the heating roller 40a and the pressure roller 40b, and when the paper passes through this fixing nip, the heating action by the heating roller 40a and the pressing action by the pressure roller 40b are applied to the paper. The toner image is fixed on the paper by receiving the toner image.

On the other hand, on the upstream side of the secondary transfer section 26 in the paper conveyance direction, a deviation detection section 42 and a positioning section 44 are provided. The offset detection section 42 outputs the amount of offset of the sheet conveyed toward the secondary transfer section 26 of the image forming section 14 . The alignment section 44 is arranged upstream of the offset detection section 42 in the sheet conveyance direction. The alignment unit 44 aligns the paper and the image based on the amount of deviation of the paper output by the deviation detection unit 42. Hereinafter, the offset detection section 42 and the alignment section 44 will be explained in more detail.

FIG. 2 is a plan view showing the configuration of the offset detection section 42 and the alignment section 44, and FIG. 3 is a diagram showing the configuration of the offset detection section 42 viewed from the upstream side in the paper conveyance direction. In FIGS. 2 and 3, the paper transport direction is the Y direction, the direction perpendicular to the paper transport direction is the X direction, and the direction perpendicular to the X and Y directions is the Z direction. The X direction and the Y direction are parallel to the paper surface of the paper transported along the paper transport path 32, and the Z direction is parallel to the thickness direction of the paper transported along the paper transport path 32. Become.

As shown in FIG. 2, the deviation detection section 42 is configured using a deviation detection sensor 85. The offset detection sensor 85 is configured by, for example, a line sensor or a CIS (Contact Image Sensor). The longitudinal direction of the offset detection sensor 85 is arranged parallel to the X direction. The offset detection sensor 85 is a reflective optical sensor having a light emitting element and a light receiving element (not shown). The offset detection sensor 85 is arranged so as to intersect (perpendicularly intersect) with one end of the sheet conveyed in the sheet conveyance direction Y. The light emitting element of the deviation detection sensor 85 emits light toward the surface of the paper at a predetermined timing when the paper being conveyed passes through the detection area of the deviation detection sensor 85. At this time, the light receiving element of the offset detection sensor 85 receives the light reflected from the surface of the paper. Thereby, the offset detection sensor 85 generates a sensor output at a level corresponding to the amount of light received by the light receiving element. The offset detection unit 42 including the offset detection sensor 85 outputs the amount of deviation between the end position of the sheet in the width direction and the reference position as the amount of offset of the sheet in the width direction of the sheet.

As shown in FIGS. 2 and 3, the alignment unit 44 includes a pair of registration rollers 81 and 82 and a drive source for swinging the pair of registration rollers 81 and 82 in the X direction (registration swing direction). A swing motor 83 is also provided. Among the pair of registration rollers 81 and 82, one registration roller 81 is a driving roller, and the other registration roller 82 is a driven roller. The registration roller 81 is made of, for example, a rubber roller, and the registration roller 82 is made of, for example, a metal roller. The registration roller 82 is always kept in pressure contact with the registration roller 81. By pressing the registration rollers 82 against the registration rollers 81, a nip portion (registration nip portion) is formed between the pair of registration rollers 81 and 82 to sandwich and convey the paper. The positioning unit 44 corrects the deviation of the paper in the width direction of the paper by holding the paper between the pair of registration rollers 81 and 82 and swinging the pair of registration rollers 81 and 82 in the X direction in this state. .

The pair of registration rollers 81 and 82 are rotatably provided by being inserted into bearings (not shown) attached to the frame 88. The registration roller 81 has a roller shaft 81b, and the registration roller 82 has a roller shaft 82b. The roller shaft 81b of the registration roller 81 and the roller shaft 82b of the registration roller 82 are connected by a connecting member 87. Thereby, when correcting the offset of the paper, the pair of registration rollers 81 and 82 swing together in the direction (X direction) orthogonal to the paper conveyance direction. A gear 81a is attached to one end of the roller shaft 81b of the registration roller 81. The gear 81a is fixed to the roller shaft 81b so as to rotate together with the roller shaft 81b. A gear 86a meshes with the gear 81a.

The registration roller 81 is connected to a drive motor 86 via a power transmission section including gears 81a and 86a. The gear 81a has a predetermined length in the X direction, which is the registration swinging direction, so that driving force is transmitted even when the registration roller 81 swings in the axial direction during the registration swinging. The gear 86a is attached to the output shaft of the drive motor 86. Thereby, the driving force of the driving motor 86 is transmitted to the registration roller 81 via the gear 86a and the gear 81a. The pair of registration rollers 81 and 82 rotates due to the transmission of this driving force. The paper conveyance operation by the pair of registration rollers 81 and 82 (driving of the drive motor 86) is controlled by the control unit 17.

Further, the registration roller 81 is connected to the swing motor 83 via a power transmission section 84 consisting of a rack 84b and a pinion 84a. That is, the power transmission section 84 and the swing motor 83 constitute the offset correction section 80 that swings the pair of registration rollers 81 and 82 in the paper width direction to correct the position of the paper in the width direction. The rack 84b is a cylindrical member having a bearing on its inner surface. The rack 84b is inserted through the roller shaft 81b. The rack 84b is fixed near the gear 81a by sandwiching both ends of the rack 84b between two washers (for example, E-rings) fixed to the roller shaft 81b. In other words, the rack 84b allows the registration roller 81 to rotate, but is fixed so as not to be able to swing in the axial direction.

Here, the amount of paper misalignment detected by the misalignment detection sensor 85 and the misalignment correction of the paper based on this amount of misalignment will be described using FIG. 4.
In FIG. 4, the position of the sheet when there is no deviation in the sheet width direction is taken as a reference position, and the value detected by the deviation detection sensor 85 at this time is taken as the detection reference value X0. In such a case, the deviation amount ΔX of the paper 50 conveyed through the paper conveyance path 32 is represented by the detection reference value X0 - the detection value Xi. In FIG. 4, the position of the transported paper 50 is shifted by ΔX to the − side (to the right in FIG. 4) with respect to the reference position. This offset amount ΔX becomes the amount of swinging of the paper (hereinafter referred to as "required swinging amount") in order to return the position of the paper 50 in the width direction to the reference position. In this case, the pair of registration rollers 81 and 82 (only the registration roller 82 is shown in FIG. 4) is swung to the + side so that one end (the left end in FIG. 4) of the paper 50 in the width direction matches the end reference position. By moving the paper, it is possible to correct the misalignment of the paper. The end reference position is a target position (swing target position) at which the end position of the paper should be aligned by the swinging operation of the pair of registration rollers 81 and 82. The end reference position is expressed as a position spaced from the image center (the center in the paper width direction) by 1/2 of the paper width W in the width direction. Further, the writing range of the image is set based on the position of the image center and the paper width W. The position of the image center and the image writing range are set, for example, when the image forming apparatus is shipped.

Detection of the amount of paper deviation by the deviation detection sensor 85 is performed for a detection compatible area of the paper. The "detection compatible area" is defined as a region that can tolerate variations in paper conveyance, and that can be detected by the paper positioning operation (registration swinging operation) performed by the positioning unit 44 before the leading edge of the paper reaches the transfer unit (secondary transfer unit 26). ) can be completed. Hereinafter, the detection compatible region will be explained in detail using FIG. 5.

In FIG. 5, in a region R1 at a distance Lx from the leading edge 50a of the paper 50, it cannot be said that the paper 50 reliably passes through the detection area of the misalignment detection sensor 85 when misalignment is detected due to variations in paper conveyance in the paper conveyance direction. It is an area. The leading end 50a of the paper 50 is the paper end on the downstream side in the paper transport direction. In this embodiment, as an example, the distance Lx from the paper leading edge 50a that defines the region R1 is 5 mm. In this case, for example, if the detection timing of the deviation detection sensor 85 is set to a position 3 mm from the leading edge 50a of the paper 50 as the predetermined distance for obtaining the deviation amount, the deviation amount of the paper cannot be detected accurately. There is a risk. On the other hand, in the region R2 after the distance Ly from the leading edge 50a of the paper 50, the distance Ly is longer than [distance from the offset detection sensor 85 to the transfer section] - [distance required for the registration swinging operation], and the registration swinging operation This is the area where the paper reaches the transfer station before the operation is complete. In this case, since the normal registration swinging operation is not performed, it is not possible to correct the deviation of the paper, and there is also a possibility that the paper may be tilted. Therefore, the region R3 whose distance from the leading end 50a of the paper 50 is equal to or greater than Lx and equal to or less than Ly becomes the detection suitable region. Further, the detection timing of the offset detection sensor 85 is set to the timing at which the distance Lz from the leading edge 50a of the paper 50 satisfies the condition "Lx≦Lz≦Ly." As a result, the deviation detection unit 42 detects a predetermined distance Lz that is preset upstream in the paper transport direction from the leading edge 50a of the paper 50 that is transported toward the transfer unit (secondary transfer unit 26) of the image forming unit 14. A position separated by a distance of 100 mm is defined as a detection target position P, and the amount of deviation of the paper in the paper width direction at this detection target position P is output. The position P where the deviation amount is detected by the deviation detection unit 42 can be determined in advance as described above by the user operating the operation display unit 20 of the image forming apparatus 10, for example, by specifying the distance Lz from the leading edge of the paper. Set.

FIG. 6 is a diagram showing the sensor output of the deviation detection sensor 85. Here, a case is shown in which the sensor output is turned on when there is paper 50, and is turned off when there is no paper 50. As shown in FIG. 6, the sensor output of the offset detection sensor 85 changes with the edge position 50b of the paper 50 as a boundary. The offset detection unit 42 recognizes the appearance position of the change point of the sensor output as the edge position 50b of the paper 50, and outputs the amount of paper offset ΔX (see FIG. 4). In addition, in the deviation detection section 42, the sensor output of the deviation detection sensor 85 is scanned in one direction, and the position where the change point of the sensor output of the deviation detection section 42 first appears is determined as the edge position of the paper 50. It is recognized as 50b.

Therefore, when the offset detection sensor 85 scans from the edge side in the paper width direction toward the center, the edge position of the paper 50 to be detected by the offset detection sensor 85, for example, as shown in FIG. If there is paper dust 55 in the vicinity of 50b, the sensor output will change due to the presence of this paper dust 55, and there is a possibility that the appearance position of this changing point will be mistakenly recognized as the edge position of the paper. In order to avoid such erroneous recognition, it is effective to scan from the center side in the sheet width direction toward the edge side with the offset detection sensor 85 as shown by the arrow in the figure. When scanning from the center side to the edge side in the paper width direction, the first change point of the sensor output appears at the edge position 50b of the paper 50, so that the sensor output is not affected by the presence of paper dust 55. The end position 50b of the paper 50 can be correctly recognized.

On the other hand, the paper used for image formation is not only plain paper, but also paper on which an image has already been formed. When forming an image on such paper, that is, when performing additional printing, if the image is formed at the above-mentioned detection target position, there is a possibility that the end position of the paper cannot be accurately detected. Specifically, as shown in FIG. 8, when the image 52 previously formed on the paper 50 to be subjected to additional printing exists at the detection target position P by the deviation detection section 42, the deviation detection sensor 85 detects the image 52. When the sensor output is scanned from the center side to the edge side in the sheet width direction, the first change point of the sensor output appears at the position of the image 52. Therefore, a position closer to the center than the original end position 50b of the paper 50 is mistakenly recognized as the end position of the paper. As a result, it becomes impossible to appropriately correct the misalignment of the paper. Furthermore, in order to appropriately correct the misalignment of the paper, it is necessary to reset the predetermined distance Lz so that the detection target position P by the misalignment detection unit 42 is set to a position other than the image 52.
When specifying reprint printing in one print job, the same image is formed in advance at the same position on a predetermined number of sheets of paper (sheets for reprinting) to be subjected to reprint printing. Therefore, by setting or resetting the predetermined distance Lz so that the offset detection target position P is at a position other than the image 52 (plain area), the edge position 50b of the paper 50 can be correctly recognized. becomes possible.

FIG. 9 is a block diagram showing a configuration example of a control system of an image forming apparatus according to an embodiment of the present invention.
As shown in FIG. 9, the image forming apparatus 10 includes the above-described paper feeding section 12, image forming section 14, paper discharging section 16, control section 17, image reading section 18, operation display section 20, paper conveyance path 32, In addition to a paper conveyance path 36, a paper discharge conveyance path 38, a fixing section 40, a swing motor 83, an offset detection sensor 85, a drive motor 86, etc., an image processing section 11, a communication section 13, and a storage section 15 are provided. There is.

The image processing unit 11 includes a circuit and the like that performs digital image processing on image data to be image formed in accordance with initial settings or user settings. For example, the image processing unit 11 performs gradation correction based on gradation correction data under the control of the control unit 17. The image processing unit 11 also performs various correction processes such as color correction and shading correction, compression processing, etc. on the image data.

The control unit 17 includes a CPU (Central Processing Unit) 21, a ROM (Read Only Memory) 23, a RAM (Random Access Memory) 25, and the like. The CPU 21 reads out a program according to the processing content from the ROM 23 or the storage unit 15, develops it in the RAM 25, and collectively controls the operation of each part of the image forming apparatus 10 in cooperation with the developed program.

Further, the control unit 17 is connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 13, and communicates with external devices (for example, a personal computer) and various types of data through this communication network. Send and receive. The control unit 17 receives, for example, a page description language (PDL) transmitted from an external device, and controls the operations of the image forming unit 14, the fixing unit 40, etc. based on the image data included in the PDL. By controlling the paper, an image is formed on the paper. Further, the control unit 17 controls the swinging operation of the pair of registration rollers 81 and 82 by driving the swinging motor 83 based on the detection result of the offset detection sensor 85. That is, the control unit 17 performs positioning of the paper and the image by correcting the deviation according to the amount of deviation output by the deviation detection unit 42. The oscillating operation of the pair of registration rollers 81 and 82 (hereinafter also referred to as "registration oscillation" or "registration oscillation") is an operation performed to correct misalignment of the paper in the paper width direction. . The communication unit 13 includes various interfaces such as a NIC (Network Interface Card), a MODEM (MOdulator-DEModulator), and a USB (Universal Serial Bus).

The storage unit 15 includes, for example, a nonvolatile semiconductor memory (so-called flash memory) or a hard disk drive. The storage unit 15 stores, for example, a look-up table LUT that is referred to when the control unit 17 controls the operation of each part of the image forming apparatus 10. One of the lookup tables LUT is a swing control table that is referred to during the offset correction process. The swing control table associates the required swing amount with a swing command value for operating the offset correction section so that the paper swings by the required swing amount. This swing control table is set at the manufacturing stage of the image forming apparatus 10, and is updated as appropriate according to the operating status of the image forming apparatus 10 (for example, the total number of printed sheets).

Referring to the swing control table stored in the storage unit 15 in this manner, the control unit 17 obtains a swing command value corresponding to the required swing amount, and controls the swing motor 83 based on this swing command value. drive Then, the rotational motion of the swing motor 83 is converted into linear motion by the pinion 84a and the rack 84b, and transmitted to the registration roller 81. As a result, the pair of registration rollers 81 and 82 swing in the axial direction by a predetermined amount (a swing amount corresponding to the swing command value). By swinging the pair of registration rollers 81 and 82 in the paper width direction while rotating, that is, while conveying the paper, the position (shifting) of the paper in the width direction is corrected. Thereby, an image can be formed at a predetermined position on the paper in the width direction of the paper.

Note that if the amount of deviation output by the deviation detection section 42 does not fall within a predetermined range, the control section 17 determines that an abnormality in deviation detection has occurred, that is, deviation correction cannot be performed. The predetermined range is set to a range in which the deviation of the sheet can be corrected by the swinging operation of the pair of registration rollers 81 and 82. Therefore, if the amount of deviation of the paper exceeds a predetermined range, the position of the paper in the width direction cannot be completely corrected. In other words, offset correction cannot be performed. In this case, the control unit 17 determines that a misalignment correction error has occurred due to an abnormality in misalignment detection, and stops the printing operation (image forming process).

As described above, the detection of the edge position of the paper (detection of the amount of deviation) by the deviation detection sensor 85 is performed for a detection target position of the paper corresponding to a predetermined distance set in advance. That is, the edge position of the paper is detected at the timing when the detection target position of the paper passes through the detection area of the deviation detection sensor 85. Furthermore, in this embodiment, as shown in FIG. 7 above, in order to avoid misrecognition due to paper dust etc. near the edge position of the paper, the sensor output of the offset detection sensor 85 is set to the center of the paper in the width direction. The position of the first change point in the sensor output that appears when scanning from the side to the edge is detected (recognized) as the edge position of the paper. In that case, as shown in FIG. 8 above, if the image previously formed on the paper to be subjected to additional printing is present at the position to be detected by the offset detection unit 42, Also, the center position will be mistakenly recognized as the edge position of the paper. For this reason, the amount of deviation of the sheet does not fall within a predetermined range, and a deviation correction error occurs due to an abnormality in deviation detection. In this case, the control unit 17 determines that the amount of deviation detected by the deviation detection unit 42 does not fall within a predetermined range, and when the deviation detection becomes abnormal, the control unit 17 determines that the paper has already been fed from the paper feed unit 12. The predetermined distance for misalignment detection is reset using the paper that has been fed and the paper that has started feeding as the fed paper. The processing contents of the control unit 17, including resetting the predetermined distance, will be explained in detail later.

A setting screen as shown in FIG. 10, for example, is displayed on the display section 20a of the operation display section 20. On this setting screen, it is possible to select a print mode, set a predetermined distance, and set an operation when an error occurs in misalignment detection. As the print mode, either the normal print mode or the reprint print mode can be selected. If the normal print mode is selected, normal printing is specified in the print job, and if the additional printing mode is selected, additional printing is specified in the print job. The predetermined distance can be set in 1 mm increments by changing the numerical value (displayed as "11" in FIG. 10) representing the distance Lz from the leading edge 50a of the paper 50 shown in FIG. 5 by operating a button. Further, the detection target position specified by a numerical value representing the predetermined distance Lz can be set within a range of 5 mm or more and 25 mm or less, which is within the range of the detection compatible region R3.

The operation when the deviation detection is abnormal can be set only when the additional printing mode is selected as the printing mode. As for the operation when the deviation detection is abnormal, it is possible to select whether or not to permit automatic updating of a predetermined distance, and it is also possible to select whether or not to permit automatic restart of the printing operation. Automatically updating the predetermined distance means automatically resetting the predetermined distance. The printing operation refers to a series of operations in which the image forming section 14 forms an image on paper supplied from the paper feeding section 12. By operating the operation display unit 20 while looking at the setting screen shown in FIG. 10, the user can select a print mode, set a predetermined distance, and set an operation when an error occurs in misalignment detection. Further, at the bottom of the setting screen, there are provided an "OK" button for confirming the contents selected or set by the user, and a "Cancel" button for canceling the contents.

By providing the operation display section 20 that displays such a setting screen on the display section 20a and receives user's operations on the operation section 20b, the user can set the desired position within the detection suitable area for the detection of offset detection. A predetermined distance can be set as the target position. Furthermore, when an abnormality in offset detection occurs, the user can cause automatic updating of a predetermined distance to be performed or not to be performed, depending on the user's own wishes. In addition, when an error occurs in misalignment detection, the user can have the printing operation automatically resumed or not, depending on the user's wishes.

Note that the setting screen shown in FIG. 10 shows a state in which the selection of the print mode, the setting of a predetermined position, and the setting of the operation at the time of abnormality of deviation detection are selected or set as follows. First, regarding the print mode, a state in which the reprint print mode is selected is shown. Further, the predetermined distance is set to a distance of 11 mm from the leading edge of the paper. Further, as the operation when the deviation detection is abnormal, "permit" is selected for automatic update of a predetermined distance, and "permit" is selected for automatic restart of printing operation.

FIGS. 11 and 12 are flowcharts showing an example of a process including detecting the amount of deviation and resetting a predetermined distance. The processing shown in this flowchart is performed under the control of the control section 17.

First, upon receiving a print job from the operation display unit 20 or an external device, the control unit 17 starts a printing operation to form an image on paper based on the image data specified in the print job (step S1). . When a printing operation is started, a sheet of paper of the size specified in the print job is sent from one of the paper feed trays 12a, 12b, and 12c to the image forming apparatus main body 30 through the paper feed conveyance path 36. The paper sent to the image forming apparatus main body 30 is transported along the paper transport path 32 by rotation of the transport roller 34. Furthermore, the image forming unit 14 starts forming a toner image at a predetermined timing based on the image data specified in the print job.

Next, on the paper conveyance path 32, when the paper passes through the alignment section 44 and the deviation detection section 42 in order, the deviation detection section 42 outputs the amount of deviation of the paper at a predetermined timing during this passage. (Step S2). At this time, if the predetermined distance is set to 11 mm from the leading edge of the paper as shown in FIG. Light emission and light reception operations are performed at corresponding timings. Thereby, the deviation detection unit 42 outputs the amount of deviation of the paper in the paper width direction at the detection target position corresponding to the currently set predetermined distance. Further, the offset detection unit 42 detects the amount of offset of the paper in the paper width direction by scanning from the center side toward the edge side in the paper width direction using the offset detection sensor 85.

Next, the control unit 17 determines whether the amount of deviation outputted by the deviation detection unit 42 is outside a predetermined range (step S3). The case where the amount of deviation is outside the predetermined range corresponds to the case where a deviation detection error occurs due to an abnormality in deviation detection. If the offset amount is within the predetermined range (No in step S3), the control unit 17 moves on to other processing and instructs the image forming unit 14 etc. to perform printing operations for the number of sheets specified in the print job. Let it run. In this case, the printed paper is discharged to the main tray 31m.

On the other hand, if the offset amount is outside the predetermined range (Yes in step S3), the control unit 17 operates the conveyance path switching unit 27 to change the paper output destination in the paper output unit 16 to the main The tray 31m is switched to the subtray 31s (step S4). The operation of switching the paper ejection destination in the paper ejection unit 16 from the main tray 31m to the sub tray 31s is an operation for ejecting the fed paper as purge paper. Purge paper refers to paper on which image formation (printing) has not been performed normally. Note that if there is a preceding sheet whose offset amount is within a predetermined range, the control unit 17 discharges the preceding sheet to the main tray 31m and then switches the sheet output destination to the sub tray 31s.

Next, the control unit 17 interrupts the printing operation by the image forming unit 14 (step S5). Next, the control unit 17 starts feeding the paper that has already been fed from the paper feeding unit 12 when the deviation amount described above does not fall within a predetermined range and the deviation detection becomes abnormal. The number of sheets of paper that has been loaded is confirmed as fed paper (step S6). Note that sheets for which offset detection has been determined to be abnormal may also be included in the fed sheets.

Next, the control unit 17 checks whether automatic updating of a predetermined distance is permitted as an operation in the event of an abnormality in deviation detection (step S7). At this time, if the user has previously operated the operation display unit 20 to select "permit" for automatic updating of the predetermined distance on the setting screen shown in FIG. It is determined that the update is permitted (Yes in step S7), and the process proceeds to step S8. Further, if the user selects "not permitted" for automatic updating of the predetermined distance on the setting screen shown in FIG. 10, the control unit 17 determines that automatic updating of the predetermined distance is not permitted ( If No in step S7), the process moves to step S14.

In step S8, the control unit 17 checks whether additional printing is specified in the print job. At this time, if the user has previously selected the additional printing mode on the setting screen shown in FIG. 10 by operating the operation display unit 20, the control unit 17 determines that additional printing has been specified. (Yes in step S8), and the process proceeds to the next step S9. Further, if the user has selected the normal print mode on the setting screen shown in FIG. Transition.

In step S9, the control unit 17 determines a position for checking deviation detection for each fed sheet so that the fed sheet is subjected to deviation detection. The position at which the deviation detection is confirmed is the position at which the amount of deviation is detected for the fed paper in order to reset the predetermined distance. The confirmation position for the deviation detection may be determined by calculation, for example, or may be determined according to a preset position. The confirmation position for offset detection is determined within the detection compatible region R3 shown in FIG. 5 above. At this time, the control unit 17 sets the number of times the deviation detection unit 42 performs deviation detection on the fed sheets and the check position of the deviation detection in accordance with the number of fed sheets.

Below, a specific method for determining the check position for misalignment detection will be explained separately for the case where one sheet of paper has been fed and the case where there are a plurality of sheets of paper. Furthermore, as a premise of the explanation, the predetermined distance that determines the position to be detected for the amount of deviation using the deviation detection sensor 85 is set to a distance of 11 mm from the leading edge of the paper by the user operating the operation display unit 20 in advance. It is assumed that this has been set. Further, it is assumed that the minimum interval in the sheet conveyance direction Y at which the amount of deviation can be detected using the deviation detection sensor 85 is 5 mm. Further, the range of the detection suitable area suitable for detecting deviation is within the range of 5 mm or more and 25 mm or less from the leading edge of the paper.

(If only one sheet of paper has been fed)
If only one sheet of paper has been fed, the amount of deviation output by the deviation detection unit 42 does not fall within the predetermined range at a position of 11 mm from the leading edge of the fed paper, and deviation detection is performed. It becomes abnormal. In this case, the control unit 17 determines positions for checking the deviation detection at intervals of 5 mm based on a predetermined distance at which the deviation detection becomes abnormal, that is, a distance of 11 mm from the leading edge of the paper. As a result, when only one sheet of paper has been fed, the positions at distances of 16 mm and 21 mm from the leading edge of the sheet are respectively determined as the positions for checking deviation detection. In this case, the predetermined distance before resetting is a distance of 11 mm from the leading edge of the paper, and the position to check for deviation detection is determined to be a position where the distance from the leading edge of the paper is longer than 11 mm. Further, the number of times the deviation is detected is set to two. Note that the distance of 11 mm from the leading edge of the paper is the same as the currently set predetermined distance, and since the deviation becomes abnormal at this distance, it is excluded from the confirmation position for deviation detection.

(If there are multiple sheets of fed paper)
When the number of fed sheets is multiple, for example four, the control unit 17 determines the distance from the leading edge of the first sheet of paper, as in the case where there is only one sheet of fed paper. The 16 mm position and the 21 mm position are determined as positions for checking deviation detection. In addition, for the second sheet of fed paper, the control unit 17 determines a distance of 5 mm from the leading edge of the paper corresponding to the minimum value of the minimum value (5 mm) and maximum value (25 mm) that define the range of the detection compatible area. Based on the distance, check positions for offset detection are determined at 5 mm intervals from there. As a result, for the second sheet of fed paper, the positions at distances of 5 mm, 10 mm, 15 mm, 20 mm, and 25 mm from the leading edge of the paper are determined as the positions for checking deviation detection, respectively. Furthermore, the number of times the deviation is detected is set to five.

In addition, the control unit 17 causes the third sheet of fed paper to be offset at intervals of 5 mm from a distance of 7 mm, which is obtained by adding 2 mm to the minimum value (5 mm) that defines the range of the detection compatible area. Determine the detection confirmation position. As a result, for the third sheet of fed paper, the positions at distances of 7 mm, 12 mm, 17 mm, and 22 mm from the leading edge of the paper are determined as the positions for checking deviation detection, respectively. Furthermore, the number of times the deviation is detected is set to four.

Furthermore, for the fourth sheet of fed paper, the control unit 17 shifts the paper at intervals of 5 mm from a distance of 9 mm, which is obtained by adding 4 mm to the minimum value (5 mm) that defines the range of the detection compatible area. Determine the detection confirmation position. As a result, for the fourth sheet of fed paper, the positions at distances of 9 mm, 14 mm, 19 mm, and 24 mm from the leading edge of the paper are determined as the positions for checking deviation detection, respectively. Furthermore, the number of times the deviation is detected is set to four.

After determining the position for checking the deviation detection in this manner, the control unit 17 determines whether or not it is possible to check the deviation detection within the paper surface of the fed paper (step S10). For example, if there is only one sheet of paper fed and the currently set predetermined distance is 23 mm from the leading edge of the paper, then when determining the check position for misalignment detection at 5 mm intervals from there, The confirmation position is outside the range of the detection compatible area (range of 5 mm or more and 25 mm or less from the leading edge of the paper). In this case, the control unit 17 determines that it is impossible to confirm the deviation detection within the paper surface of the fed paper. Also, when there are multiple sheets of fed paper, and the predetermined distance currently set for the first fed paper is 23 mm from the leading edge of the paper, the control unit 17 , it is determined that it is impossible to confirm the deviation detection. On the other hand, for the second and subsequent sheets of fed paper, the check position for misalignment detection can be determined within the range of the detection compatible area, so the control unit 17 It is determined that it is possible to confirm the deviation detection. If it is determined that it is possible to check the deviation detection within the paper surface of the fed paper (Yes in step S10), the process proceeds to step S11, and if it is determined that it is impossible (No in step S10). Then, the process moves to step S14.

In step S11, the deviation detection unit 42 outputs the deviation amount at all the determined confirmation positions for the fed paper based on the control command from the control unit 17. For example, when there is only one sheet of fed paper, the deviation detection section 42 outputs the amount of deviation at distances of 16 mm and 21 mm from the leading edge of the paper.

Next, the control unit 17 checks whether or not there is a confirmation position where the deviation amount falling within a predetermined range is obtained from among the deviation amounts output by the deviation detection unit 42 in step S11. (Step S12). Then, if at least one of the one or more offset amounts output in step S11 falls within a predetermined range, the control unit 17 determines Yes in step S12 and proceeds to the process of step S13. If all the deviation amounts are out of the predetermined range, it is determined No in step S12 and the process moves to step S14.

In step S13, the control unit 17 stores in the storage unit 15 the distance information of the confirmation position where the amount of deviation falling within a predetermined range is obtained. For example, when there is only one sheet of fed paper, if the offset amount falls within a predetermined range at both a distance of 16 mm and a distance of 21 mm from the leading edge of the paper, the control unit 17 The information is stored in the storage unit 15. Distance information is distance information that allows you to specify the confirmation position where the amount of deviation that falls within a predetermined range is obtained. For example, when specifying the confirmation position by the distance from the leading edge of the paper as in this embodiment, The value of the distance from the tip may be stored in the storage unit 15.

Thereafter, in step S14, the paper discharge section 16 discharges the fed paper onto the subtray 31s based on a control command from the control section 17. As a result, the fed paper for which deviation detection has been confirmed is discharged to the subtray 31s as purge paper. Therefore, by visually checking the fed paper discharged to the sub-tray 31s, the user can understand that reprint printing has not been performed normally.

Next, the control unit 17 determines whether all the fed sheets have been discharged (step S15). When the control unit 17 has discharged all the fed sheets of the number confirmed in step S6 above to the subtray 31s, the control unit 17 determines Yes in step S15 and proceeds to the process of step S16. Further, if there are any fed sheets remaining that have not been discharged to the sub-tray 31s, the control unit 17 determines No in step S15 and returns to the process of step S7. As a result, if there are a plurality of sheets of fed paper, the processes of steps S7 to S14 are applied to each fed sheet of paper. Therefore, if there are four sheets of paper fed, the first sheet of paper will be offset at a distance of 16 mm and 21 mm from the leading edge of the paper, as in the case of one sheet of fed paper. The detection unit 42 detects the amount of deviation. Further, for the second sheet of fed paper, the deviation detection section 42 outputs the deviation amounts at distances of 5 mm, 10 mm, 15 mm, 20 mm, and 25 mm from the leading edge of the paper. In addition, for the third sheet of fed paper, the deviation detection unit 42 outputs the amount of deviation at distances of 7 mm, 12 mm, 17 mm, and 22 mm from the leading edge of the paper, and for the fourth sheet of fed paper, In contrast, the offset detection unit 42 outputs the amount of offset at distances of 9 mm, 14 mm, 19 mm, and 24 mm from the leading edge of the paper.

After that, in step S16, the control unit 17 checks whether reprint printing is specified in the print job. If additional printing is not specified (No in step S16), the series of processes ends at that stage. Further, if reprint printing is specified (Yes in step S16), the control unit 17 resets a predetermined distance based on the distance information stored in the storage unit 15 in step S13 (step S17).

At this time, the control unit 17 extracts the shortest distance from the leading edge of the paper from among the distance information stored in the storage unit 15, and resets the extracted distance as a predetermined distance. For example, if the distances of 7 mm, 15 mm, 17 mm, 22 mm, and 24 mm from the leading edge of the paper are stored as distance information in the storage unit 15, the control unit 17 will reproduce the distance of 7 mm from the leading edge of the paper as the predetermined distance. Set. As a result, when correcting the misalignment of the paper by the paper alignment operation (registration swinging operation) of the alignment unit 44, the predetermined distance is adjusted according to the distance with a large margin of time for misalignment correction. Can be set. Furthermore, when performing reprint printing, even if the detection target position P corresponding to the predetermined distance before resetting is set to the position where the image 52 exists, as shown in FIG. After resetting, the detection target position can be set to a position where the image 52 does not exist.

In addition, in the present embodiment, when determining the confirmation position for misalignment detection in step S9, the positioning unit 44 determines the position of the paper before the leading edge of the paper reaches the secondary transfer unit 26 of the image forming unit 14. The position for checking the deviation detection is determined within the area where the alignment operation (registration swinging operation) can be completed, that is, within the detection compatible area. Therefore, in step S17, the control unit 17 resets the predetermined distance so that the detection target position of the deviation detection amount exists within the detection suitable area. Therefore, by detecting the amount of deviation detected at the detection target position corresponding to the predetermined distance after resetting, the positioning unit 44 can be detected before the leading edge of the paper reaches the secondary transfer unit 26 of the image forming unit 14. Paper alignment operations can be completed reliably.

After that, the control unit 17 checks whether automatic restart of the printing operation is permitted as an operation when the deviation detection is abnormal (step S18). At this time, if the user has previously operated the operation display unit 20 to select "permit" for automatic restart of the printing operation on the setting screen shown in FIG. If it is determined that permission is granted (Yes in step S18), the printing operation by the image forming unit 14 or the like is restarted (step S19), and the series of processing ends. When restarting the printing operation, the control unit 17 resets the print page count value. Thereby, in the reprint printing mode, the printing operation can be restarted from the first page. Further, if the user selects "not permitted" for automatic restart of printing operations on the setting screen shown in FIG. 10, the control unit 17 determines that automatic restart of printing operations is not permitted (in step S18). No), the series of processing ends at that stage.

As described above, the image forming apparatus 10 according to the embodiment of the present invention determines that deviation correction cannot be performed as a result of outputting the amount of deviation by the deviation detection sensor at a predetermined distance set in advance. In this case, the deviation detection sensor outputs the amount of deviation by changing the predetermined distance, and the predetermined distance is reset based on the output result. According to this configuration, the predetermined distance for detecting deviation can be reset without having the image reading unit 18 read the paper before printing. Therefore, the effort required to reset the predetermined distance can be reduced. When the image reading unit 18 reads the paper before printing, if the orientation of the paper to be read is incorrect, there is a risk that additional printing will be performed with the predetermined position setting inappropriate. Well, there is no such fear. Furthermore, in this embodiment, since the predetermined distance can be appropriately changed using fed paper, machine stoppages due to errors in misalignment detection can be suppressed, contributing to improved productivity. be able to.

Note that in the reprint printing mode, it may not be possible to reset the predetermined distance depending on the position of the image previously formed on the reprint paper. In such a case, the control section 17 disables the positioning operation function of the positioning section 44. Furthermore, after disabling the positioning function, the control unit 17 automatically restarts the printing operation by the image forming unit 14 and the like. For example, when the predetermined distance cannot be reset, an image is formed with a high area ratio in the detection compatible area R3 (see Figure 5) of the paper for reprinting, and all of the check positions for offset detection are This is a case where the amount of deviation outputted by the deviation detection section 42 at the confirmation position is all out of the predetermined range because of the presence of the image.

In this way, when the predetermined distance cannot be reset, the function of the positioning operation by the positioning unit 44 is disabled, thereby preventing a malfunction of the positioning unit 44 due to an abnormality in deviation detection. be able to. In addition, by automatically restarting the printing operation after disabling the positioning function, it is possible to reduce machine stoppage time due to errors in misalignment detection and improve image forming productivity. . Note that if you disable the alignment function when the predetermined distance cannot be reset, the image quality will deteriorate because the image and paper will not be aligned; Since the distance is approximately several mm, it is acceptable if high image quality is not required.

<Modified examples, etc.>
The technical scope of the present invention is not limited to the embodiments described above, but also includes various modifications and improvements within the scope of deriving specific effects obtained by the constituent elements of the invention and their combinations.

For example, in the above embodiment, a case has been described in which the pair of registration rollers 81 and 82 function as a positioning section, but the present invention is not limited to this. In this case, the image may be aligned with the paper by adjusting the image forming position when the exposure device forms the electrostatic latent image on the surface of the photoreceptor.

14... Image forming section 17... Control section 26... Secondary transfer section (transfer section)
42... Offset detection section 44... Alignment section 50... Paper 50a... Tip 81, 82... Registration roller 85... Offset detection sensor Lz... Predetermined distance R3... Detection compatible area

Claims (20)

an image forming unit that forms an image on paper;
A deviation detection sensor disposed upstream of the image forming section in the paper transport direction detects the amount of deviation in the width direction of the paper at a position a predetermined distance away from the leading edge of the paper in the paper transport direction. an offset detection section that outputs
a control unit that aligns the paper and the image by misalignment correction according to the amount of misalignment;
As a result of outputting the amount of deviation by the deviation detection sensor at the predetermined distance that has been set in advance, when the control unit determines that deviation correction cannot be performed, the control unit changes the predetermined distance and outputs the deviation amount again. An image forming apparatus, wherein the deviation detection sensor outputs the deviation amount, and the predetermined distance is reset based on the output result. The image forming apparatus according to claim 1, wherein the control unit determines that the deviation correction cannot be performed when the deviation amount outputted by the deviation detection unit does not fall within a predetermined range. The image forming apparatus according to claim 2, wherein the predetermined range is a range in which misalignment of paper can be corrected. A registration roller is disposed upstream of the image forming section in the paper conveyance direction,
The image forming apparatus according to claim 2 , wherein the predetermined range is a range in which misalignment of the sheet can be corrected by the swinging operation of the registration roller. Image forming according to claim 4, wherein the control unit corrects the deviation of the paper so that the edge position of the paper in the paper width direction matches a reference position by swinging the registration roller in the paper width direction. Device. The image forming apparatus according to any one of claims 2 to 5, wherein the control unit resets a distance at which an offset amount falling within the predetermined range is obtained as the predetermined distance. The control unit causes the deviation detection unit to output the deviation amount again from the predetermined distance at a plurality of different distances, and selects a position where the deviation amount falling within the predetermined range is obtained. The image forming apparatus according to claim 2, wherein the predetermined distance is reset to a distance corresponding to the shortest distance from the tip of the image forming apparatus. Claims 1 to 7, wherein the control unit causes the deviation detection sensor to output the deviation amount again by changing the predetermined distance for the fed paper that has already started feeding. The image forming apparatus according to any one of the above. 8. The control unit sets the number of times the misalignment detection unit performs misalignment detection on the fed sheets and the check position for misalignment detection according to the number of fed sheets. The image forming apparatus described in . The image forming apparatus according to claim 8 , wherein the control unit causes the deviation detection unit to output the deviation amount for each of the fed sheets when there is a plurality of the fed sheets. . The image forming apparatus according to claim 8, wherein the fed paper is discharged as purge paper. The image forming apparatus according to any one of claims 1 to 11, further comprising an operation display unit that can set the predetermined distance. The image forming apparatus according to any one of claims 1 to 12, further comprising an operation display unit that allows selection of whether to permit resetting of the predetermined distance. The image forming apparatus according to any one of claims 1 to 13, wherein the control unit resets the predetermined distance when reprint printing is specified in a print job. The deviation detection unit outputs the deviation amount by scanning the deviation detection sensor from the center side in the paper width direction toward the edge side. image forming device. The image forming unit includes a transfer unit that transfers an image to paper,
The image according to any one of claims 1 to 15, wherein the control unit resets the predetermined distance within a region where the paper alignment operation can be completed before the leading edge of the paper reaches the transfer unit. Forming device. The image forming apparatus according to claim 16, wherein the control unit disables the paper alignment function when the predetermined distance cannot be reset. The image forming apparatus according to any one of claims 1 to 17, wherein the control section automatically restarts the printing operation by the image forming section after resetting the predetermined distance. The image forming apparatus according to claim 17, wherein the control section automatically restarts the printing operation by the image forming section after disabling the function of the sheet alignment operation. The image forming apparatus according to claim 18 or 19, further comprising an operation display section that allows selection of whether or not to automatically restart the printing operation.

Images